JP5459973B2 - Sample inspection equipment - Google Patents

Description

  The present invention relates to a sample inspection apparatus for analyzing a semiconductor sample or the like and a method for creating an absorption current image using the sample inspection apparatus, and more particularly to a technique for identifying an electrical failure location in wiring of a semiconductor sample or the like.

  In a semiconductor sample in which a circuit is formed on a semiconductor surface, it is difficult to specify a defective portion as the device is miniaturized, and the failure analysis requires a great deal of time. Therefore, analysis devices such as OBIRCH (Optical Beam Induced Resistance Change) and EB tester are currently used.

  In the semiconductor sample defect analysis, as a defect analysis related to wiring, in recent years, an electron beam is irradiated on the surface of a semiconductor sample, and a current absorbed from the wiring or a secondary signal emitted from the semiconductor sample is analyzed / imaged. Is attracting attention.

  For example, in Patent Document 1, in a semiconductor sample on which a wiring pattern is formed, a probe is brought into contact with both ends or one side of the wiring pattern, an electron beam is scanned over the wiring pattern on the semiconductor sample, and a current flowing through the probe is detected. A technique for identifying a defective portion by measuring / imaging the image is disclosed.

  Patent Document 2 discloses a technique for amplifying signals from a plurality of probes, taking a difference between the signals, scanning the differential amplified signal to display an image, and modulating and scanning an irradiation electron beam, Similarly to the above, a technique for scanning a differential amplification signal and displaying an image is disclosed.

JP 2002-368049 A JP 2003-86913 A

  As described in the above prior art, an image generated from currents input from a plurality of probes represents an absorption state of charged particles in a sample. In general, a defective part can be found by analyzing this absorption current image. However, when the resistance component of the defective part is low or the target wiring is complicated, the brightness of the defective part and the normal part is reduced. It becomes difficult to make a difference and it becomes difficult to identify the location. A technique for facilitating identification of a defective portion is necessary.

  Also, by changing the optical conditions of the charged particles, an absorption current image having a different depth direction is acquired. For example, when there is a disconnection in the depth direction, the absorption current image of a certain depth is There will be no signal. It is difficult to find this change by looking at two or more two-dimensional images, and it is not intuitive to explain the state to a third party. There is a need for an image display method that intuitively shows defects such as wiring in the depth direction.

  Further, when the probe is brought into contact with the sample, if the sample surface is charged or there is a potential difference between the probe and the sample surface, a discharge phenomenon occurs between the probe and the sample at the time of contact. In some cases, damage may remain to the probe and the sample. The same phenomenon occurs when charged particle images are continuously acquired over a long period of time. Therefore, electrical protection of the sample and the probe is necessary.

  A first object of the present invention is to provide an inspection apparatus that facilitates identification of a defective portion using an absorption current image detected using a plurality of probes.

  The second object of the present invention is to provide an inspection apparatus for displaying a defective part in an easier-to-see image.

  The third object of the present invention is to protect the sample and the probe during the probe operation in the inspection apparatus.

  In general, the defective portion is considered to have some resistance value. When the temperature of the sample changes, this resistance value tends to change. Therefore, if you look at the image of the difference between the absorption current images (in a sense, the absorption voltage image) when the temperature is changed, the brightness change due to the resistance change of the defective part appears remarkably, and the defective part can be identified. Can be easily done.

  Images obtained by adding and subtracting weighted images of multiple images generated by changing the location of the probe, and images obtained by adding and subtracting weighted images of multiple images generated by changing the electro-optic conditions, The brightness change of the defective part appears remarkably, and the defective part can be easily identified.

  In addition, since a plurality of images with different imaging conditions may have different positions, if a weighted image is added or subtracted after performing position correction, the resulting image is also a defective portion. A change in brightness appears remarkably, and it becomes possible to easily identify a defective portion.

  Furthermore, a cross-sectional image at an arbitrary position can be reproduced by using a plurality of absorption current images obtained by changing the optical conditions of the charged particles and having information on the depth direction of the sample and displaying them in a three-dimensional manner. Since it becomes possible to comprise, it is possible to display the cross-sectional image of a defect location. Thereby, the defective part in a depth direction can be displayed intuitively. It is also easy to identify.

  Also, if the sample surface is charged or there is a potential difference between the probe and the sample surface, a discharge phenomenon may occur between the probe and the sample during contact. Since damage sometimes occurs, the optical condition of the charged particles is automatically lowered to a predetermined condition when the probe is moved. For example, the acceleration voltage is lowered, or the emission current or probe current is lowered. As a result, the potential between the sample and the probe can be reduced, and damage to the probe and the sample due to discharge or the like can be prevented.

  Further, when the probe is moved, the probe is electrically switched to the ground level of the apparatus to make it difficult for discharge or the like to occur. When the movement and contact can be confirmed, the electrical connection of the probe is restored, and the electron optical condition for irradiating the sample is also restored to the original charged particle condition. Even when images are acquired continuously over a long period of time, the same phenomenon may occur, so change the optical conditions and the electrical level of the probe in the same way. In this case, the sample and the probe can be electrically protected.

  Furthermore, the charged state of the sample is detected by a detector, and the sample is irradiated with an electron beam under an electron optical condition that cancels it, or the potential level of the probe is set to the same potential as the charged state of the sample. Carry out needle contact in a state where discharge is unlikely to occur. After the probe contacts, the potential accumulated on the surface can be relaxed by dropping the potential of the surface to the ground level.

  According to the present invention, even when it is difficult to discriminate a defect portion from an absorption current image, it becomes easy to identify the defect portion by looking at the change in the image of the temperature change of the sample and the change in the optical conditions.

  In addition, according to the present invention, the location of a defect has been difficult to identify in a two-dimensional image until now, but a defective position can be intuitively recognized by reconstructing a cut-out image from a three-dimensional image.

  Further, according to the present invention, it is possible to reduce the discharge of the sample and the probe that may occur when the probe is moved.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of a sample inspection apparatus to which an embodiment of the present invention is applied.

  The primary electron beam 1 is applied to the sample 2. A wiring pattern 3 is provided on the surface of the sample 2, and the probe 4 is brought into contact with one side or both ends of the wiring pattern 3 or a pad. In this state, the surface of the sample 2 including the wiring pattern 3 is scanned with the primary electron beam 1 from the electron beam source 5.

  Of the irradiated primary electron beam 1, electrons flowing into the wiring pattern 3 are detected as current from the probe 4 and input to the amplifier 6 for amplification. The amplifier 6 generates and outputs a signal with respect to the input signal. This signal is synchronized with the scanning of the primary electron beam 1 and is displayed on the display unit 8 as an absorption current image 7.

  The sample is heated and cooled by the sample heating / cooling unit 9 below the sample 2. At that time, the position of the defective portion can be emphasized and identified by weighting addition / subtraction of the plurality of acquired absorption current images 7. When performing weighted addition / subtraction of an image, addition / subtraction is performed after correcting the position and magnification of the image. Although the present invention has been described in a system that can perform both heating and cooling, the present invention is not limited to this, and can be applied to the case where only one is possible.

  FIG. 2 shows the inside of the vacuum chamber 16 in cross section. Below the sample 2 is a sample holder 19 on which the sample is placed, and a heater 11 for heating and a temperature sensor 14 for detecting the temperature are incorporated in the sample holder receiving portion 13 below the sample holder 19. The temperature sensor and the heater are controlled by the temperature controller 15, and the temperature of the sample 2 is kept constant. By using this system and acquiring a plurality of absorption current images 7 when the temperature of the sample 2 is changed, and performing weighted addition and subtraction of the images, the location of the defective portion can be remarkably emphasized.

  If the coloring is changed by the numerical value of the weighted image, the defective portion can be further emphasized.

  FIG. 3 shows weighted addition and subtraction expressions for a plurality of absorption current images. Two absorption current images are added and subtracted by weighting constants w and g. The two images may be an image of a sample with a change in temperature, an absorption current image in which the electro-optical conditions are changed, or an absorption current image in which the position where the probe contacts is changed.

FIG. 4 is an equation when the weighted addition / subtraction of the two images in FIG. 3 is expanded to three or more images.
Examples of images with different temperatures are displayed when K = 2.

  FIG. 5 describes an example of a simple difference between two images having different sample temperatures. By taking the difference image, the portion where the contrast has changed due to the temperature change is emphasized.

  Here, the weighting coefficient may be determined so that the pixel values at the same position of the image at the sample temperature A ° C. and the image at the sample temperature B ° C. have the same size.

  If this position is a defect position, the pixel values at places other than the defect position remain in the image obtained by weighting and taking the difference, and the defect position is also emphasized after all.

  FIG. 6 shows that in order to identify a short-circuited portion in parallel wiring, a probe is applied to a plurality of locations to obtain an absorption current image at that time, and the contrast of the short-circuited portion is enhanced by weighted subtraction of the plurality of absorption current images. There is an example of that.

  Note that not only the temperature change but also the weighted addition / subtraction of the absorption current image in which the electro-optic conditions are changed can be similarly performed to emphasize the defective portion.

  When images under two different conditions are acquired, the center position of the image may be shifted or the magnification may be changed, and there are cases where addition and subtraction cannot be used simply. In such a case, for example, the amount of image misregistration is calculated by the least square method, the phase only correlation method, or the like, and weighted addition and subtraction are performed with the pixel values shifted from each other. When the positional deviation is a real number, addition and subtraction are performed in proportional divisions after the decimal point. The magnification may be adjusted by comparing the magnifications using feature portions in the image.

  The absorption current image acquired while changing the electron optical conditions, for example, the acceleration voltage, becomes an image having depth information from the sample surface. FIG. 8 superimposes acquired image groups while changing the acceleration voltage and the current amount, and acquires an arbitrary cross-sectional image using 3D clipping software.

  Pixel data of an arbitrary cross section is obtained by proportional interpolation calculation of pixel data of adjacent two-dimensional images.

  By cutting out the tomographic plane, it becomes possible to check the wiring defect in the vertical direction, which is difficult to see in the horizontal image, as a two-dimensional image in the vertical direction, leading to a reduction in the identification time of the defect in the depth direction. .

  FIG. 9 shows a case where five images with different electro-optical conditions are overlaid. In the horizontal image, only the third line from the top can recognize the wiring. In the fourth and fifth sheets, the wiring is considered to be disconnected. If the cross-sectional images of the five superimposed images are cut out by 3D image processing and the cross-sectional images are cut out, it can be confirmed in one image at which position in the vertical direction the wiring is disconnected.

  Also in this case, if a three-dimensional image is formed after correcting the positional deviation amount of the image described in the fourth embodiment, a clear defect position can be specified.

  If the sample surface is charged or there is a potential difference between the probe and the sample surface, a discharge phenomenon may occur between the probe and the sample during contact, causing damage to the probe or the sample. Since the remaining case may occur, when the probe is moved, the function of automatically reducing the optical condition of the charged particle to a certain condition is set.

  FIG. 10 is an example of an operation flowchart for moving the probe. When moving the probe, the optical conditions of the charged particles are automatically changed to a function that drops to a certain condition. For example, the acceleration voltage is changed to a lower one, and the emission current and the probe current are changed to lower conditions. As a result, the potential between the sample and the probe can be reduced, and damage to the probe and the sample due to discharge or the like can be prevented.

  Thereafter, the probe is moved. When the movement is completed, the electron optical conditions immediately before that are automatically restored. That is, the acceleration voltage is increased and the irradiation current is increased.

  In this state, an absorption current image is acquired, and when it is desired to change the condition, the absorption current image is acquired by changing to a new optical condition.

  In the flowchart of FIG. 11, in addition to the conditions of FIG. 10, when the probe is moved, the electro-optical condition is changed in a direction in which the discharge phenomenon does not occur, but in addition, the probe potential is also changed.

  This flowchart will be described with reference to FIG. After the electro-optic condition is changed, the switch of the signal switching unit 10 is used to switch the probe so that it is connected to the ground terminal instead of being connected to the conventional amplifier. By switching the probe potential to the ground level, the probe can be brought into contact with the surface of the sample more safely.

  When the movement of the probe is completed, the probe is automatically switched from the ground connection to the amplifier, and the electro-optical condition is automatically returned to the original state. Thereafter, the flow is to acquire an absorption current image.

  The case where the probe potential change is further advanced will be described using the same flowchart shown in FIG. FIG. 12 shows a case where the charge detector 17 for measuring the potential of the surface of the sample 2 is also provided. The charge detection is, for example, a measuring device using a capacitance.

  When the probe is moved, the electron optical conditions are automatically changed to a lower value for the sample as in the seventh embodiment. Thereafter, the surface potential of the sample is measured using a charge detector, and the same potential as that potential is output to the charge control potential output meter.

  The signal switching unit 10 is switched from the amplifier connection to the charging control potential output meter to change the probe potential. Move the probe to contact the sample. Since the probe potential and the sample potential are the same, discharge can be prevented. When the contact is confirmed, the output of the charging control potential output meter 18 is lowered to the ground level. Thereby, the potential of the sample can be lowered to the ground level. If there is no electrical difference between the probe and the sample, damage to the probe and the sample due to discharge or the like can be prevented.

  Further, by changing the output of the charging control potential output meter 18 to an arbitrary voltage level, the potential state of the wiring portion changes, and the way of emitting secondary electrons changes. As a result, the image contrast of the defective portion changes, and the efficiency of the defect analysis can be improved.

1 is a schematic configuration diagram of a sample inspection apparatus to which an embodiment of the present invention is applied. 1 is a schematic cross-sectional view of a sample inspection apparatus to which an embodiment of the present invention is applied. It is explanatory drawing of weighted addition and subtraction of two images to which an embodiment of the present invention is applied. It is explanatory drawing of weighted addition and subtraction of a plurality of images to which an embodiment of the present invention is applied. It is explanatory drawing of the weighting addition and subtraction of the image with a temperature difference with which one Embodiment of this invention is applied. It is explanatory drawing of weighting addition and subtraction of the image from which the probe contact position differs by which one Embodiment of this invention is applied. It is explanatory drawing of the weighting addition and subtraction of a different image when there exists position shift to which one Embodiment of this invention is applied. It is explanatory drawing of the cross-section cutout by 3D software with which one Embodiment of this invention is applied. It is explanatory drawing of the defect position identification of the cross-section cutout by 3D software with which one Embodiment of this invention is applied. It is explanatory drawing of the flow in which the electro-optical conditions at the time of the probe position change to which one Embodiment of this invention is applied change. It is explanatory drawing of the flow from which the electron optical conditions at the time of the probe position change to which one Embodiment of this invention is applied change, and the electric potential of a probe also change automatically. 1 is a schematic configuration diagram of a sample inspection apparatus in which an electron optical condition at the time of changing a probe position to which an embodiment of the present invention is applied is changed, and a probe potential is also automatically changed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary electron beam 2 Sample 3 Wiring pattern 4 Probe 5 Electron beam source 6 Amplifier 7 Absorption current image 8 Display part 9 Sample heating / cooling part 10 Signal switching part 11 Heater 12 Movable stage part 13 Sample holder receiving part 14 Temperature sensor 15 Temperature Controller 16 Vacuum chamber 17 Charge detector 18 Charge control potential output meter 19 Sample holder

Claims (15)

A charged particle source;
A charged particle beam optical system for irradiating a sample with a charged particle beam emitted from the charged particle source;
A detector for detecting secondary electrons emitted from the sample;
A probe in contact with the sample;
In the sample inspection apparatus for forming an image based on a signal from the probe,
A sample image is formed based on the current flowing into the probe by irradiation with the charged particle beam,
Acquiring the sample images at a plurality of different sample temperatures;
A sample inspection apparatus, wherein a new image is formed by adding or subtracting signals of the plurality of sample images. The sample inspection apparatus according to claim 1,
A sample inspection apparatus, wherein a new image is formed by adding or subtracting an image signal weighted for a part or all of a plurality of sample images having different temperatures. The sample inspection apparatus according to claim 1 or 2,
A sample inspection apparatus using an image obtained by correcting the alignment and / or magnification of each sample image for the plurality of sample images. A charged particle source;
A charged particle beam optical system for irradiating a sample with a charged particle beam emitted from the charged particle source;
A detector for detecting secondary electrons emitted from the sample;
A probe in contact with the sample;
In the sample inspection apparatus for forming an image based on a signal from the probe,
A sample image is formed based on the current flowing into the probe by irradiation with the charged particle beam,
Acquiring the sample image under conditions of a plurality of different charged particle optical systems;
A sample inspection apparatus, wherein a new image is formed by adding or subtracting image signals of the plurality of sample images. The sample inspection apparatus according to claim 4, wherein
A sample inspection apparatus, wherein the conditions of the different charged particle optical systems are changed by changing an acceleration voltage, a charged particle dose, and a charged particle beam incident angle of a charged particle source irradiated on the sample. The sample inspection apparatus according to claim 4, wherein
A sample inspection apparatus, wherein a new image is formed by adding or subtracting an image signal weighted for a part or all of the plurality of sample images. In any one of the sample inspection apparatuses of Claim 4 thru | or 6,
A sample inspection apparatus using an image obtained by correcting the alignment and / or magnification of each sample image for the plurality of sample images. A charged particle source;
A charged particle beam optical system for irradiating a sample with a charged particle beam emitted from the charged particle source;
A detector for detecting secondary electrons emitted from the sample;
A probe in contact with the sample;
In the sample inspection apparatus for forming an image based on a signal from the probe,
A sample image is formed based on the current flowing into the probe by irradiation with the charged particle beam,
Acquiring the sample image at a plurality of different probe positions;
A sample inspection apparatus, wherein a new image is formed by adding or subtracting image signals of the plurality of sample images. The sample inspection apparatus according to claim 8, wherein
A sample inspection apparatus for acquiring a sample image by bringing a probe into contact with a different position on the wiring of the sample. The sample inspection apparatus according to claim 8 or 9,
A sample inspection apparatus, wherein a new image is formed by adding or subtracting an image signal weighted for a part or all of the plurality of sample images. In any one of the sample inspection apparatuses of Claim 8 thru | or 10,
A sample inspection apparatus using an image obtained by correcting the alignment and / or magnification of each sample image for the plurality of sample images. A charged particle source;
A charged particle beam optical system for irradiating a sample with a charged particle beam emitted from the charged particle source;
A detector for detecting secondary electrons emitted from the sample;
A probe in contact with the sample;
In the sample inspection apparatus for forming an image based on a signal from the probe,
A sample image is formed based on the current flowing into the probe by irradiation with the charged particle beam,
The sample image is obtained by focusing the charged particle beam at different positions in the depth direction of the sample,
A sample inspection apparatus for forming a new image having a plane perpendicular to the sample image by superimposing the plurality of sample images in a sample depth direction and complementing a signal amount between the sample images. The sample inspection apparatus according to claim 12, wherein
By changing the acceleration voltage and charged particle dose of the charged particle source irradiated to the sample,
A sample inspection apparatus, wherein conditions of the different charged particle optical systems are changed. The sample inspection apparatus according to claim 12 or 13,
A sample inspection apparatus, wherein a new image is formed by adding or subtracting an image signal weighted for a part or all of the plurality of sample images. In any one of the sample inspection apparatuses of Claim 12 thru | or 14,
A sample inspection apparatus using an image obtained by correcting the alignment and / or magnification of each sample image for the plurality of sample images.

Images